Free electron laser (FEL) systems require the use of electromagnetic undulators or wigglers. In an FEL system, transfer of energy takes place from the primary electron beam to a radiation wave in the medium of an alternating magnetic field developed within either an undulator or a wiggler assembly. In a similar manner, undulators or wigglers are essential in the implementation of an Inverse-Free Electron Laser Particle Accelerator (IFELA) system. For a typical IFELA, the transfer of energy is made from an intense radiation wave to an electron beam while the beam is colinearly traversing the undulator or wiggler assembly. It is possible to achieve a high energy gain per unit length within such an electron accelerator. An IFEL electron accelerator may make use of a quasi-sinusoidal magnetic field, with constant maximum field amplitude, and with varying undulator or wiggler lengths. Depending upon the beam injection energy into such an IFEL linear accelerator, this so-called period length may vary from a few centimeters up to several times such a period length for given assemblies.
Although such a structure could possibly be constructed using presently known techniques, employing permanent magnet material, the resultant cost of manufacture would be very high because of the non-repeat feature of the undulator or wiggler length. The use of conventional direct current electromagnetic excitation of undulator or wiggler assemblies by means of a multiplicty of individual pole coils is excluded from such design considerations, because of the small value of the period length at beam injection for a typical set of IFELA parameters.